The present invention relates to jet engines, and, in particular, relates to jet engines having afterburners, and, in greater particularity, relates to cooling of the liner therein.
Typical afterburners are provided with a liner whose function is to produce a film of cooling air to protect the nozzle flow path components from the hot exhaust gases. While this approach maintains allowable metal temperatures, large quantities of cooling air are required which reduce its efficiency. Another problems with this type of liner is the warping and other distortion that occur due to thermally induced stresses resulting from attaching a hot liner to a cooled casing. This distortion causes variations in the cooling efficiency and the warped surface decrease the sealing efficiency. A fourth problem is hot streaks. The hot streaks can cause metal temperatures to rise locally by several hundred degrees compared to the average temperature. The current cooling systems provide a constant air flow to each area. Since it is unable to compensate for local hot streaks, the entire duct and nozzle are cooled as if under hot streak conditions. Since the actual hot streaks cover a minority of the surface area, most of the area is receiving excess cooling air. There are also areas of the sidewall which are exposed to hot flow only at certain nozzle positions such as maximum jet area or thrust vectoring. These areas receive unneeded flow at other times.
Thus there is a need for active cooling means to locally tailor the cooling air flow to local conditions thus allowing all of the liner area to operate at design temperatures.